The invention relates to relief valves for relieving excess pressure from fluid pressurized systems.
A conventional pressure relief valve in its simplest form includes a valve seated by an adjustable compression spring against the force of the fluid pressure of the system it protects. More sophisticated designs include internal mechanisms which require adjustment when the system fluid is changed. However, when adjusted for one fluid, such valves tend to become unstable when called on to handle another. In addition, repeat accuracy of the set or blow-off point is difficult to achieve in large spring-loaded valves because of non-uniform heating of the large, set-pressure adjustment spring. Pilot-controlled relief valves which utilize low-lift pilot control stages have been evolved to overcome certain of the functional problems of large valves, but pilot valve leakage in such designs could cause premature operation.
Accordingly, among the objects of the present invention are the provision of a relief valve design which is capable of consistent operation with a wide variety of system fluids; the provision of a reliable relief valve in which the seating force increases in direct proportion to increasing system pressure until the pressure set for blow-off is reached; and the provision of a relatively leak-free valve, the operation of which is characterized by full opening pop action.
A further object of the invention is to provide readily serviceable relief valve design for high pressure systems in which the control of the main relief valve is effected through pilot valve controls which, together with the main valve, are self-actuated by the fluid pressure of the system. A further object of the invention is to provide a relief valve assembly, the action of which is controlled by the pilot-control valve means which are themselves highly insensitive to leakage to such an extent that a substantial leak in the control system will not result in the inadvertent operation of the main pressure relief valve.
A further object of the invention is to provide a relief valve design such that the valve will open by direct action of the fluid pressure on the main valve and will relieve at the rated capacity in the event of failure of any essential part of the pilot valve.